The quest to develop larger and larger semiconductors of the dynamic random access memory (DRAM) type is a well-known goal. The industry has steadily progressed from DRAMs of the 16K type, shown in U.S. Pat. No. 4,081,701 issued to White, McAdams and Redwine, and the 64K type, shown in U.S. Pat. No. 4,055,444 issued to Rao, to DRAMs of the 1M type, as described in U.S. Pat. No. 4,658,377 issued to McElroy. DRAMs of the 4M type are now being produced. Production plans for 16M DRAMs of submicron technology now exist and experimentation of 64M DRAMs has begun. One factor furthering the development of larger DRAMs is the reduction in memory cell geometries as illustrated in U.S. Pat. No. 4,240,092 to Kuo (a planar capacitor cell), and as illustrated in U.S. Pat. No. 4,721,987 to Baglee et al, (a trench capacitor cell).
One difficulty in fabricating high density integrated circuit structures such as DRAMs is filling the contact holes, or vias, with metal so that electrical contact may be made to the integrated circuits. U.S. Pat. No. 4,673,592 to Porter et al. discusses this difficulty and describes a metal planarization process to reliably fill deep depressions having high aspect ratios. In order to minimize space, the aspect ratios of contacts become even higher as memory cell geometries continue to decrease. It becomes even more difficult to fill these high aspect ratio contacts with conductive material.
It is thus an object of this invention to provide a method for packing high aspect ratio via contacts with metal. It is also an object of this invention to provide an improved contact structure.
Other objects and advantages of this invention will be apparent to those of ordinary skill in the art having reference to the following specification and drawings.